1. Field of the Invention
The present invention relates to an image communication apparatus, method, and system, and an image communication processing program contained in a computer-readable medium and, more particularly, to a technique of communicating image data using asynchronous TDMA (Time Division Multiple Access).
2. Related Background Art
Conventionally, when a plurality of radio (wireless) stations are to perform asynchronous data communication with partner stations by using carrier waves with the same frequency, each of the stations time-divisionally communicates by TDMA (Time Division Multiple Access).
FIG. 1 shows a conventional communication protocol and a data packet format.
Referring to FIG. 1, before communication, the transmission station performs carrier sense to check for a predetermined time whether a radio wave is being sent from another station, thereby avoiding interference between the radio wave from the self station and that from another station. If no radio waves from other stations are detected within the carrier sense time, communication is started; otherwise, carrier sense is continued.
If no radio waves from other stations are detected, the transmission station sends a request to send (RTS) signal to the partner station (station on the reception side). Upon receiving the RTS, the partner station sends a clear to send (CTS) signal for allowing transmission. When a CTS is received within a predetermined waiting time Tw after sending the RTS, the transmission station waits for a predetermined rise time for AGC (Automatic Gain Control) of the partner station and then transmits data packetized into a predetermined packet format.
Each packet has a header portion and a data portion including image or audio data. The header portion is made up of a synchronization signal (SYNC) and a portion including the partner station ID, a unique word representing the start of reception, a status, and a checksum.
Upon completing 1-packet data transmission, the transmission station transmits another RTS. When a CTS is received within the predetermined waiting time Tw, the transmission station transmits packet data again after the elapse of the AGC rise time. For image data, the above operation is repeatedly performed such that an image for one frame or one field is sent as a plurality of packets.
In the above-described conventional communication protocol, however, since RTS/CTS hand shaking is done for each packet, a waiting time Tw is generated for each packet. If another station interrupts during this time Tw, the interrupt and the CTS from the partner station collide. The CTS does not reach the transmission station, and the transmission station cannot send data. Especially, when image data for one picture is to be transmitted, and transmission is stopped due to an interrupt from another station, a partially omitted image is displayed on the monitor on the reception side. Even when the omitted portion is interpolated by a previously stored image, continuity of the image is impaired.
In addition, conventionally, since the header portion in the same data format is sent in units of packets, the packet length increases, and a long time is required to send an image for one frame.
An object of the present invention is to solve the above-described problems.
It is another object of the present invention to realize, in an image communication apparatus, processing of radio-transmitting image data for one picture in a short time without interruption.
As a preferred embodiment for such objects, according to the present invention, there is provided an image communication apparatus comprising:
generation unit for generating a plurality of communication packets from image data for one picture; and
communication unit for continuously radio-transmitting the plurality of communication packets, output from the generation unit, through a radio transmission channel shared by a plurality of devices.
It is another object of the present invention to realize, in an image communication method, processing of radio-transmitting image data for one picture in a short time without interruption.
As a preferred embodiment for such objects, according to the present invention, there is provided an image communication method comprising the steps of:
generating a plurality of communication packets from image data for one picture; and
continuously radio-transmitting the plurality of communication packets through a radio transmission channel shared by a plurality of devices.
As another embodiment of the present invention, there is provided an image communication method comprising the steps of:
performing carrier sense in a radio transmission channel shared by a plurality of devices for a predetermined time;
transmitting a transmission request to a destination in accordance with a carrier sense result; and
continuously transmitting a plurality of communication packets formed from image data for one picture upon detecting a response to the transmission request within a predetermined time.
It is still another object of the present invention to realize, in an image communication system, processing of radio-transmitting image data for one picture in a short time without interruption.
As a preferred embodiment for such objects, according to the present invention, there is provided an image communication system comprising:
a transmission apparatus and a reception apparatus,
wherein the transmission apparatus performs carrier sense in a radio transmission channel shared by a plurality of devices, and transmits a transmission request to the reception apparatus in accordance with a carrier sense result,
the reception apparatus returns a response to the transmission request when processing corresponding to the transmission request can be performed, and
the transmission apparatus continuously transmits a plurality of communication packets formed from image data for one picture to the reception apparatus upon detecting the response to the transmission request within a predetermined time.
It is still another object of the present invention to realize, in an image communication processing program contained in a computer-readable medium, processing of radio-transmitting image data for one picture in a short time without interruption.
As a preferred embodiment for such objects, according to the present invention, there is provided an image communication processing program contained in a computer-readable medium, comprising:
a program code for generating a plurality of communication packets from image data for one picture; and
a program code for continuously radio-transmitting the plurality of communication packets through a radio transmission channel shared by a plurality of devices.
As another embodiment, there is provided an image communication processing program contained in a computer-readable medium, comprising:
a program code for performing carrier sense in a radio transmission channel shared by a plurality of devices for a predetermined time;
a program code for transmitting a transmission request to a destination in accordance with a carrier sense result; and
a program code for continuously transmitting a plurality of communication packets formed from image data for one picture upon detecting a response to the transmission request within a predetermined time.
Still other objects of the present invention, and the advantages thereof, will become fully apparent from the following detailed description of the embodiments.